A neutron generator may include an ion source and a target. An electric field is generated within the neutron generator that accelerates the ions toward the target at a speed sufficient such that, when the ions are stopped by the target, neutrons are generated and emitted into a formation into which the neutron generator is placed. The neutrons interact with atoms in the formation, and those interactions can be detected and analyzed in order to determine information about the formation.
While well logging instruments utilizing these neutron generators are useful, they suffer from some unfortunate drawbacks. For example, commonly used ion sources may emit conductive particles that may build up on insulating surfaces inside the neutron generator, thereby changing the characteristics of those insulating surfaces. This in turn may undesirably affect the electric field inside the neutron generator, and therefore alter the focus point of the ion beam, which may result in the ion beam not striking the intended portion of the target. The foregoing serves to degrade the performance of the neutron generator, and thus the performance of the well logging instrument utilizing the neutron generator.
Another drawback is that some ions generated by the ion generator may be neutralized by interactions with gases inside the neutron generator. These energetic neutral particles may impinge on a conductive electrode surface, ejecting charged particles such as electrons, and conductive particles such as sputtered metal that could land on an insulator, creating a layer on the insulator which may be charged and may be conductive.
As such, further advances in the area of neutron generators are desirable. It is desired for such new neutron generators to reduce the buildup of undesirable charged or conductive particles on insulating surfaces, and thus provide a high degree of stability and consistency, such that they can deliver a tightly focused ion beam to the target and consistently generate neutrons.